This is volume 95 in the Very Short Introduction series published by Oxford University Press. I suppose it was worth reading, although I expected more about particular ideologies as opposed to the general nature of ideology.
Freeden defines a political ideology as: “a set of ideas, beliefs, opinions and values that
(1) exhibit a recurring pattern
(2) are held by significant groups
(3) compete over providing and controlling plans for public policy
(4) do so with the aim of justifying, contesting or changing the social and political arrangements and processes of a political community.”
He identifies four main political ideologies (socialism, liberalism, conservatism and fascism) but argues convincingly that none of them can be precisely defined. What they share are general commitments to certain fundamental principles, which can also be understood as preferred ways of applying certain key terms. For example, a liberal and a fascist may both be in favor of “freedom” and “justice” but define those terms differently and apply them to different situations.
Freeden doesn’t think that having an ideology is a bad thing. He clearly favors some ideologies over others, but suggests that having a political ideology is like having fundamental principles or preferences, and that it’s almost inescapable to have an ideology if you take politics seriously. At least in the Western world, the four mentioned above, although they have evolved through the years, have been the most frequently adopted.
Throughout the book, Freeden emphasizes the importance of language in the study of ideology:
Ideologies compete over the control of political language as well as competing over plans for public policy; indeed, their competition over plans for public policy is primarily conducted through their competition over the control of political language.